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The threat to Campbell Live, which has prompted widespread public concern, is symptomatic of a deeper structural malaise in New Zealand's media sector.

MediaWorks' concern is not primarily Campbell Live's rating lower than Seven Sharp but its marginal returns and capacity to deliver audience flow to subsequent programmes.

Even if Campbell Live were out-rating Seven Sharp, the relentless drive to maximise returns from every slot could make it economically rational to replace it with a programme that is cheaper or more popular.

Moreover, Sky's acquisition of Prime TV has increased free-to-air competition and driven up the cost of acquiring key contents rights packages which are crucial to remaining competitive in prime-time.

This leaves less money for local content and other niche genres.

The competition to acquire the high-rating premium programmes will only intensify with the emergence of subscriber video-on-demand (SVOD) providers like Netflix and Lightbox.

The result will be a concentration of similar content formats as commercial schedulers all pursue the same demographics and advertising dollars.

Public concerns about the abolition of the TVNZ Charter and the closure of the commercial-free channels TVNZ 6 and 7 were dismissed.

The Government asserted that in the digital environment, public service institutions were irrelevant and NZ On Air's contestable funding model would compensate for market failures and ensure quality and diversity.

A decade ago, there was competition for substance as well as audience at 7pm: Holmes was replaced by Close-Up; TV3 started Campbell Live; Prime recruited Paul Holmes to head a third evening current affairs show.

But the virtuous public service circle has now turned commercially vicious.

Close-Up has given way to the breakfast-style Seven Sharp.

Only two programmes survive on free-to-air from TVNZ 6 and 7 - Back Benches on Prime and Media Take, now on Maori TV (after TV3 rejected a new series).

Hundreds of thousands of viewers watch Campbell Live every week and many who are not regular viewers nevertheless value the provision of news and current affairs on the occasions when the events affect their lives.

Many Cantabrians will testify to the role the show has played in keeping their plight on the public agenda and holding those in power to account.

But if commercial logic is allowed to drive the entire television sector, we will likely be left without any regular, substantive current affairs in prime time.

That would be a tragedy for democracy.

We have a right as citizens to a robust fourth estate and news and current affairs that holds those on power to account.

If the market cannot provide this, the Government must take some responsibility and explore how it might establish a multi-platform, public service free-to-air channel to provide genuine diversity and quality in the digital era.